|Species: Wilson’s Warbler
Wilson’s Warbler is
named after the ornithologist Alexander Wilson, who first described
it in 1811, aptly titled as pusilla comes from the Latin term for
‘very small’. It is a common and widespread wood warbler found
across Canada: the breeding range extends from Alaska to Newfound
Land and partway down the western coast and Rocky Mountain region of
the US. A neotropical migrant, it flies at night overland to its
wintering home in Central America, going as far as western Panama;
interestingly, it defends its winter territory with as much vigour
as it does during the breeding season. This bird is also the only
migrant warbler regularly found in the tropical high grasslands.
“Wilson” is also the mascot for the Vancouver Avian Research
Identification: Wilson’s Warbler is a rather small songbird,
about 10-12 cm in length and weighs around 8 grams. It has a long,
thin tail and short, rounded wings, pinkish legs and feet and a
small, dark-coloured bill.
Adult Male: The male is an unmarked and bright yellow
underneath, darker olive-yellow on top, and has a distinguishing
glossy, solid black cap (which extends across the crown with age).
While his face is generally bright, the auriculars and nape are dark
olive; wings and tail feathers are also dark, but edged with
Adult Female: The mature female looks very similar to the
adult male, but her cap is usually only partial, duller and mottled
with olive, and her face may be a paler yellow than that of the
Juvenile: The juvenile male looks similar to the adult
female, with flecks of yellow in his black crown, and is less bright
overall than the adult male. Juvenile females have a mottled
green-yellow crown, with relatively few black specks.
Similar Species: The Yellow Warbler is an overall bright
yellow, and is distinguished by the reddish streaks down its breast
and the absence of the black cap. The Orange-crowned Warbler is a
much drabber yellow, with some faint streaking on its breast.
Behavior: Quite an active little bird, the Wilson’s Warbler
frequently hops about, characteristically raising and flicking its
tail. For feeding, it usually forages within 10 feet of the ground
(but rarely on it), gleaning twigs and leaves for small insects and
spiders (but includes berries in its diet as well). This bird also
actively flycatches for its prey (note the rictal bristles at the
base of its bill)!
Habitat: Generally preferring riparian habitat, this bird is
usually found in willow and alder thickets near water, wet woodlands
and shrubby fields, and often keeps low in the bushes. Its voice, a
rapid and chattering chchchchchchch, a common song heard in the
spring here in Vancouver, might give it away first!
Being a widespread
species, Wilson’s Warblers will nest anywhere from sea level to
alpine; they build a cup-shaped nest using ground vegetation such as
moss, grass and leaves. Usually the nest is placed on the ground,
hidden by a clump of grass, but Pacific coastal lowland birds tend
to place their nests low in shrubs. The female builds the nest
herself and she will incubate the eggs for an average of 12 days;
the clutch typically consists of 3-6 cream-white eggs with
There are three subspecies of this bird that are currently
recognized and W. p. chryseola is the one found in Vancouver and
along the Pacific coast. An interesting note, western birds tend to
have more yellow on the face than do their eastern cousins.
The longevity record for a wild Wilson’s Warbler is a male at 6.8
It holds a status
of Least Concern, but this is being kept under close watch, as there
seems to be a downward trend - particularly in western populations,
most likely due to large-scale habitat loss. It does, however, do
quite well in shade-grown coffee plantations!
Although caught in every month from April through October,
capture rates (2010-2012; standardized as birds captured per
100 net hours) of Wilson's Warbler go through a large peak
in May as they pass through Colony Farm to their nearby
breeding areas. As long distance migrants, these warblers
move south for the winter as seen by our zero capture rates
between November and March.